1. Field of the Invention
This invention relates to an insert adapted to be molded into a molded plastic part in order to effect a fluid-tight seal between the plastic part and another object to which the plastic part is to be fastened. This invention has particular application to providing a fastening ring insert molded into a plastic tank in order to form a leakproof, fluid-tight connection between the tank and an object which closes or communicates with the interior of the tank.
2. Background Art
In many applications, it is necessary for plastic parts, such as fuel tanks, to be able to be readily and repeatedly fastened and unfastened to other objects, yet also be able to maintain a fluid-tight seal when fastened.
Prior art devices, such as that disclosed in U.S. Pat. No. 4,023,257, have used a fastening insert molded into a plastic container. These fastening inserts generally are flat washers or similar devices which contain either male or female connectors. The washers are, for example, an aluminum ring of approximately a 5 inch outer diameter and a 4 inch inner diameter. The washers are connected to the inside of the mold used to form the container. The washer is placed in the mold so that it will form an essentially flat surface, flush with the outside wall of the molded article. During the molding process, the plastic material surrounds or encapsulates the washer and the connectors.
As the molded article is cooled and cured, however, the plastic material tends to shrink around the connectors and form slight depressions between adjacent connectors, thus inhibiting the ability of the insert to maintain a flat sealing surface and effect a fluid-tight connection. The prior art inserts also tend to flex during the molding process, which prevents the insert from forming a flat, fluid-tight sealing surface. This flexibility also limits the practical size of the inserts, since the larger the insert the greater its tendency to flex during the molding process.
In order to overcome the problems of obtaining a fluid-tight seal with a fastening insert molded into a plastic part, it is common to use a sealing gasket between the parts to be joined. Sealing gaskets, however, usually do not provide a surface flat enough to seal effectively.